[Bug tree-optimization/103399] New: [12 Regression] Wrong code with -O2

[Bug tree-optimization/103399] New: [12 Regression] Wrong code with -O2

[vsevolod.livinskij at frtk dot ru]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103399

            Bug ID: 103399
           Summary: [12 Regression] Wrong code with -O2
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vsevolod.livinskij at frtk dot ru
  Target Milestone: ---

Link to the Compiler Explorer: https://godbolt.org/z/3GE6fKvYr

Reproducer:

#include <stdio.h>
char a = 0;
long long b[8][10][18];
void e(int, long long[][10][18]) __attribute__((noipa));
void e(int f, long long g[][10][18]) {
  for (int d = 0; d < f; d += 3LL)
    for (int c = 0; c < ((f ? g[5][0][0] : 0) ^ g[5][0][0]) + 1; c++)
      a = 42;
}
int main() {
  for (size_t i = 0; i < 8; ++i)
    for (size_t k = 0; k < 10; ++k)
      for (size_t j = 0; j < 8; ++j)
        b[i][k][j] = -1311387439415292401LL;
  e(8, b);
  printf("%u\n", a);
  if (a != 42)
    __builtin_abort();
}

Error:
>$ g++ -O1 driver.cpp && ./a.out
42
>$ g++ -O2 driver.cpp && ./a.out
0

gcc version 12.0.0 20211123 (721d8b9e26bf8205c1f2125c2626919a408cdbe4) (GCC)

[Bug tree-optimization/103399] [12 Regression] Wrong code with -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103399

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.0

[Bug tree-optimization/103399] [12 Regression] Wrong code with -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103399

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-11-24

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed reduced testcase:
int t1 = -2;
int e(int) __attribute__((noipa));
int e(int f) {
    int t = 0;
  for (int d = 0; d < f; d ++) {
    for (int c = 0; c < ((f ? t1 : 0) ^ t1) + 1; c++)
      t= 42;
  }
 return t;
}
int main() {
  unsigned a = e(1);
  printf("%u\n", a);
  if (a != 42)
    __builtin_abort ();
}

Note the t1 being negative is important. t1 being global is also important, if
you do a load of t1 before either loop, you end up with working code.

THis is another bswap issue ...

[Bug tree-optimization/103399] [12 Regression] Wrong code with -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103399

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Before bswap, we have:
  iftmp.0_11 = t1;
  t1.1_1 = t1;
  _2 = t1.1_1 ^ iftmp.0_11;

But after we get:
  load_dst_8 = MEM[(int *)&t1];
  _2 = (int) load_dst_8;

Which is wrong as _2 should have been 0.

[Bug tree-optimization/103399] [12 Regression] Wrong code with -O2

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103399

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|NEW                         |RESOLVED

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 103376.

*** This bug has been marked as a duplicate of bug 103376 ***